Balancing standard for propeller blades



March 1935. .1. H. M KfiE ,9

BALANCING STANDARD FOR PROPELLER BLADES Filed April 1, 1932 Patented Mar. 5, 1935 BALANCING STANDARD FOR PROPELLER BLADES James H. McKee, Pittsburgh, Pa., assignor to- Pittsburgh Screw &Bolt Corporation, a corporation of Pennsylvania I Application April 1, 1932, Serial No. 602,544-

tachable propeller blades.

5 In the manufacture of detachable propeller is of the utmost importance that the blades be so constructed that they will be exact duplicates of each other so that they will be readily interchangeable. To secure interchangeability 10 of the blades it is necessary that the blades be in That is, that .one transverse portion of one blade exactly balances a liketransverse portion of the opposed blade.

e blades are conmass of all transon a straight line tation of the 'problades it static and dynamic balance To secure static balance, th 15 structed so that the centers of verse sections of the blade'fall at right angles to the axis of ro peller hub. Heretofore to determine whether a detachable ,adjustable propeller blade was in one of the sockets of a suitable hub and balanced against a standknown in the art positioned in the h a metlfod of se- 20 static balance it was placed in ard blade of the same design,

as the master blade, which was opposedzsocket of the hub. Suc

' curing the static balance of detachable propeller blades has not proven entirely satisfactory because the master blade, although manufactured with extreme care, is never in perfect balance because of the fact that it is impossible under the 30 present conditions and shop practices, to make such a master blade having the necessary curvature and varying thicknesses for different transverse sections which has the center of mass of each section'on a straight line extending longi- 35 tudinally of the blade. As a result of not having a true standard against which each of the detachable blades is balanced, it is apparent that the blades balanced thereagainst were not in perfect balance, and blades balanced against one master blade would not necessarily be in balance with blades balanced against another master blade of the same design, because the two master blades themselves would not be in balance witheach other.

pparatus for of balance in de- Claims. (01. 7341 ical propelcenters of mass of each section of the blade will fall on the same line as the centers of mass of the standard A further object is to provide accurate means for obtaining the required balance indetachable 5 propeller blades. I

A still further object is to provide an accurate standard for use in balancing detachable propeller blades.

These and other objects which will be'made obvious to those skilled in this particular art are attained by means of this invention, one embodiment of which is described in the following specification and illustrated in the accompanying drawing, wherein:

Figure 1 is a.- top plan view partially in-section, showing a hub having a blade mounted therein for balancing, and a testing standard involving my invention against which the blade is balanced, and- -Fig. '2 is a top plan view, partially in section, of a propeller hub having a modified form of testing standard attached thereto.

Referring to the drawing in detail, 10 indicates a propeller hub having opposed sockets 11 and 12' extending radially therefrom for receiving the ends of detachable propeller blades. Mounted in the socket 11 is a testing standard 13 made in accordance with my invention and against which to be statically balanced.

The testing standard 13 comprises a hollow precision made tube 15 having one end. lfl so shaped that it will be readily received in the blade receiving socket 11. The wall of the tube 15 is of uniform thickness throughout and the sides of the tube are so constructed that the inner and outer walls thereof are straight and parallel to each other so that the center of mass of any transverse section of the tube falls on substantially the same straight line which, when the tube is positioned in the socket 11, is at right angles to the axis of rotation of the hub 10.

The exterior surface of the tube 15 is'threaded one object of tfiis invention is to provide anas at 17 and has two steel rings or discs or nuts paratus with which it is possible to secure precision of balance in detachable propeller blades whereby duplicate, interchangeable blades may be readily manufactured.

Another object is to provide a testing standard for balancing propeller blades having the centers of mass of each, section thereof on a straight line at right angles to the axis of rotation whereby it will be possible to so balance propeller blades by adding metal thereto-that the 18 and 19 threaded thereon and having a com-' mon axis with the tube so that the centers of mass of the, nuts 18 and 19 are on substantially the same line asthe center of mass of the tube 15. The nuts .18 and 19 may be locked in position on the tube 15 bytuming them in opposite directions.

To statically balance the blade 14, the nuts 18 I and 19.are first locked on. the tube in a position I a blade 14 mounted in the opposed socket 12 is so I 13 as having an end ily flt in the sockets of any ard'is in the form of a 2 to give the proper static balance to a blade of the size and length of the blade to be balanced.

When these nuts 18 and 19 have been set in proper position on the tube 15, the hub 10 is rotatablFmounted' on a spindle (not shown) so that it is free to turn therearound. Weights are then added to the exterior of the blade 14 until it is in both horizontal and vertical balance with the standard 13. thus statically balanced, the blade is removed and metal, equal in weight to the weights placed on the blade to secure the horizontal and ,vertical balance, is added to the proper portions of the blade at which time the blade will be in static balance with the precision made master testing standard 13.

While I have illustrated the testing standard 16 which is shaped to be received in the socket 11, it is to be'understood that the standard 13 may be formed integral with the hub 10, if it is so desired. It is also understood when the standard is made separately, the end 16 maybe so shaped that it will readtype or propeller hub. For example, in Figure 2 I have shown a testing standard 20 of the same construction as the testing standard 13 but having the end modified as at 21 so that it will be readily receivable in a socket 22 on another type of propeller hub 23. The, hub 23 has an opposed socket 24 in which a blade 25 is adapted to be fitted for the purpose of being statically balanced against the standard 20 as previously described.

From the foregoing description it is readily apparent that I have provided a testing standard in which all of the centers of mass of the various sections'of the standard fall on the same straight line, which when the standard is mounted in a hub, is at right angles to the axisof rotation of the hub, and blades may be so balanced thereagainst that the centers of mass of transverse sections thereof will be on the same straight line as the center of mass of the standard. As a result the blades are the exact duplicates of one another and are readily interchangeable with eachother.

It is also readily apparent that since the standtube or annular member, it is possible to readily produce a standard which is extremely accurate and by the use of concentric rings, one which may beused to balance all types and designs of detachable propeller blades. While I have described one modification of my tion or the scope When the blade 14 has been invention it is to be understood that certain changes and modifications may be made therein without departing from the spirit of my invenof the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. A testing standard for use in .statically balancing detachable propeller blades comprising'a tubular member of uniform wall thickness having an end adapted to be received in one of the sockets of a propeller hub, and annular members concentrically and movably mounted on said tubular member.

2. A testing standard for balancing detachable propeller blades comprising an arm havin an end adapted to be received in one of the sock- ,ets of a propeller hub, said arm being substantially circular in cross section and having the centers of mass of each section located on substantially the same straight line, and annular members threaded on the periphery of said arm and having their centers of'mass on substantially the same line as the centers of mass of the arm.

3. Apparatus for statically balancing detachable hollow propeller blades comprising a propeller hub having a socketfor receiving the shank of a blade to be balanced, a tube extending radially from said hub on the opposite side thereof from said socket, and weight members on said tube having a common axis therewith, said tube and weight members forming a standard against which the blade is balanced.

, 4. Apparatus for statically balancing a detachable propeller blade comprising a-hub having a socket for receiving the end of the blade to be balanced, an annular member extending from said hub on the opposite side thereof from said blade receiving socket and having substantially all the centers of mass of each transverse section thereof on a line at right angles to the axis of rotation of said hu ,and means on said member for determining the static balance of the blade to be balanced.

5. Apparatus for statically balancing detachable propeller blades, comprising a propeller hub having a socket for receiving the shank of a blade to be balanced and an arm-extending radially from said hub on the opposite side thereof from said socket, said arm having the center of mass of each transverse section located substantially on a straight line perpendicular to the axis of rotation of said hub.

' JAMES H McKEE. 

